1. Technical Field
The present invention relates in general to a radio telephone system and in particular to a method and system for allocating frequencies for fixed location radio telephones. Still more particularly, the present invention relates to a method and system for frequency planning for a communication system comprised of fixed wireless application.
2. Description of the Related Art
Evolving nations are implementing telephone based communication systems. It has been determined that the most economical method for installing a telephone system where no previous system exists is to designate a fixed base wireless telephone for each subscriber.
A Fixed Base Radio Telecommunication (FBRT) topology is commonly referred to as Fixed Wireless Application (FWA) or Wireless Local Loop (WLL). FWA and WLL allow a telephone company to take advantage of the wireless technology as a substitute for the last several miles of transmission line to bring telephony into a household and to users. The economic attractiveness of FBRT is enormous.
A telephone company will save the investment to lay down copper transmission lines in dense, and congested city streets and buildings. FWA and WLL also decreases the time to bring telephony service to demanding consumers.
FWA and WLL applications are novel because handoff requirements are greatly reduced because radio telephones remain within a fixed location (i.e. within a relatively small geographic area). In mobility application, handoff is an operational necessity to allow intra-cell roaming (sector-to-sector and within the same cell), and inter-cell roaming (roaming between cells).
Handoff is accomplished according to the technology utilized. For example, analog communication or digital communication require different handoff procedures. In digital technology, the type of communication is also important. Types of digital technology communication include Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA). Digital technologies allow a higher number of subscribers to be simultaneously serviced. Hence, digital technology provides a communication system within a higher bandwidth.
A CDMA system utilizes soft handoff (SHO) to provide seamless, xe2x80x9cmake-before-breakxe2x80x9d transition for inter-cell roaming. SHO minimizes the forward and reverse link power requirement via antenna diversity.
In a FBRT system, users are stationary by definition. Except for users in the vicinity of a cell edge, most user profiles can be optimized to see a single dominant pilot signal and thus the percentage of SHO is greatly reduced. For users who are close to the cell edge or do not have adequate coverage, directional antennas can be prescribed to improve the communication link. In a FWA or a WLL, the requirements for SHO can be greatly minimized. However, due to fading and other phenomena SHO procedures cannot be entirely eliminated in a FBRT system.
In general, CDMA technology does not require a frequency plan as in Advanced Mobile Phone Service (AMPS), Time Division Multiple Access (TDMA), and Global System for Mobile communications (GSM) implementations. Each cell/sector utilizes the same carrier frequency and identifies itself via the PN (Pseudo-random Number) sequence offset. Thus, a mobile radio telephone only receives and transmits on an assigned PN sequence offset.
In a CDMA system, softer handoff is utilized for inter-sector roaming and soft handoff is utilized for inter-cell roaming. A CDMA is distinguished from conventional radio telephone technology. In conventional systems tele-traffic bearing capacity is limited by frequency (channel) allocation. Whereas tele-traffic bearing capacity in a CDMA system is limited by interference. Categorically, interference within a CDMA system can arise from many sources. A robust frequency plan requires analysis of interference possibilities.
In a CDMA cellular system, each base station not only receives interference from radio telephones in the home cell (intra-cell interference), but also from radio telephones in neighbor cells (inter-cell interference).
CDMA technology allows each cell to utilize the same frequency. Thus, when a mobile roams from cell to cell the mobile radio telephone is not required to change its transmit and receiver frequency.
Hence, interference arises in both the down-link (base stations to radio telephones) and up-link(radio telephones to base stations) directions. The impact to inter-cell and intra-cell interference are the most significant components of the overall interference constraints.
Another interference source is adjacent channel interference. The transition from AMPS to CDMA is emerging in the 800 MHz frequency band. CDMA cells overlay pseudo noise on existing AMPS cell site networks. Adjacent channels interference from AMPS channels and co-channel interference from AMPS channels from far away cells is possible. Generally, channel interference from far away cells is not significant and hence, is not considered. However, Adjacent Channel Interference (ACI) from microwave incumbents can cause significant interference.
The microwave incumbent interference can create a problem for CDMA systems in the 1900 MHz PCS frequency spectrum. Historically, the point-to-point microwave backhaul utilizes the 1900 MHz frequency band. However, the microwave incumbent is typically very localized and its impact is restricted to a very few selected number of cells/sectors.
The Federal Communication Commission (FCC) often requires microwave incumbents to relocate to other spectrum if radio telephone interference occurs. This trend is likely to continue in the future. In the 800 MHz spectrum microwave incumbents are not a significant problem.
Intermodulation interference both from same block (same operator) and different blocks (different operators) and thermal noise floor are also sources of undesirable interference. The effect of the third order intermodulation interference and thermal noise floor are considered to be independent of the number of sectors within a cell.
Thus, the impact of third order intermodulation interference and thermal noise floor are invariant to the configuration of sectorization. Hence, for a FWA or WLL sectorization method the impact of third order intermodulation interference and thermal noise floors is negligible.
Therefore, there is a need for a method for frequency planning for fixed wireless telephone applications. It would be also be desirable to provide a CDMA system frequency planning method which can increase the communication bandwidth, reduce the interference and increase the frequency reuse factor for a CDMA communication system.
It is therefore one object of the present invention to provide an improved radio telephone system.
It is another object of the present invention to provide a method and system for allocating frequencies for fixed location radio telephones.
It is yet another object of the present invention to provide a method and system for frequency planning a communication system comprised of fixed base radio telephones.
The foregoing objects are achieved as is now described. A method for evaluating frequency plans for a CDMA based communication system having fixed base radio telephones is provided. The method begins by determining locations of a plurality of antennas. The plurality of antennas provide a coverage area for radio telephones. Then the method generates locations of radio telephones within the coverage area. Next, a distance from each radio telephone to the antennas is calculated. Then frequencies are allocated to the antennas. The resulting communication parameters between the radio telephones and the antennas are evaluated. Next, the coverage area which provides increased power control to each radio telephone is determined. A frequency reuse factor is calculated to determine the efficiency of the allocated frequencies such that frequency allocation plans can be analyzed to determine efficient frequency planning.
The above as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.